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United States Patent |
5,716,701
|
Skoglund
,   et al.
|
February 10, 1998
|
Pressure-sensitive adhesive compositions having improved peel force
retention on flexible vinyl substrates
Abstract
This adhesive for laminating vinyl face stock to solid substrates has good
initial peel strength, retains peel strength and is emulsion polymerized
and compounded in the absence of sodium or lithium cations.
Inventors:
|
Skoglund; Michael J. (Dublin, OH);
Lee; Shang (Dublin, OH)
|
Assignee:
|
Ashland Inc. (Russell, KY)
|
Appl. No.:
|
419215 |
Filed:
|
April 10, 1995 |
Current U.S. Class: |
428/355AC; 428/461; 428/463; 428/520; 428/522; 428/523 |
Intern'l Class: |
C09J 007/02 |
Field of Search: |
428/355,461,463,522,523,520,355 AC
|
References Cited
U.S. Patent Documents
2976203 | Mar., 1961 | Young et al.
| |
4822676 | Apr., 1989 | Mudge.
| |
5069942 | Dec., 1991 | Anderson.
| |
5316762 | May., 1994 | Kiamil.
| |
5368843 | Nov., 1994 | Rennie.
| |
Foreign Patent Documents |
5548321A1 | Mar., 1992 | EP.
| |
57-143373 | Sep., 1982 | JP.
| |
Other References
The Applications of Synthetic Resin Emulsions, H. Warson, Ernest Benn
Limited, London 1972.
Development of Acrylic Latex Pressure Sensitive Adhesive for Plasticized
PVC Films, Journal of Plastic Film & Sheeting, vol. 2--Apr. 1986.
Handbook of Adhesives, Second Edition, edited by Irving Skeist, copyright
1977 by Litton Educational Publishing, Inc.
Production Information, Pressure Sensitive Latexes, UCAR Latex 173 (Sep.
1982).
Polymers, Resins and Monomers, Rohm and Haas Company, 1982.
Rohm and Haas Company, Experimental Emulsion E-1031, Acrylic Emulsion for
Pressure-Sensitive Adhesives (no date available).
Polymers, Resins and Monomers, RHOPLEX Pressure Sensitive Acrylic Emulsions
for Adhesive Formulators, Rohm and Haas Company, 1987.
|
Primary Examiner: Davis; Jenna
Attorney, Agent or Firm: Picken; Mary E.
Claims
We claim:
1. A laminate of flexible vinyl face stock, pressure sensitive adhesive
film, and metal substrate, said laminate having initial PSTC 1 peel
strength, PSTC 1 peel strength retention on aging, said film consisting of
the dried residue of an aqueous emulsion pressure sensitive adhesive
copolymer of alkyl acrylates, styrene, and acrylic acid polymerized in the
substantial absence of sodium or lithium cations in the presence of
ammonium group containing surfactant.
2. A laminate of flexible vinyl face stock, pressure sensitive adhesive
film, and metal substrate, said laminate having initial PSTC 1 peel
strength; PSTC 1 peel strength retention on aging, said film consisting of
the dried residue of an aqueous emulsion pressure sensitive copolymer of
alkyl acrylates, styrene and acrylic acid compounded using an ammonium
group containing surfactant to a coater ready adhesive in the substantial
absence of sodium or lithium cations.
3. A laminate of flexible vinyl face stock, pressure sensitive adhesive
film, and metal substrate, said laminate having initial PSTC 1 peel
strength, PSTC 1 peel strength retention on aging, said film consisting of
the dried residue of an aqueous emulsion pressure sensitive adhesive
emulsion copolymer of alkyl acrylates, styrene and acrylic acid
polymerized in the substantial absence of sodium or lithium cations using
an ammonium group containing surfactant and compounded into a coater ready
adhesive in the substantial absence of sodium cation or lithium cation.
4. The laminate of claim 3 comprising plasticized vinyl face stock.
5. The laminate of claim 3 wherein said adhesive is emulsion polymerized
and compounded in the presence of ammonium cation.
6. The laminate of claim 3 wherein said adhesive composition contains less
than 150 parts Group 1 metal cation per million parts dry weight.
7. The laminate of claim 1 wherein said surfactant is the ammonium salt of
nonyl-4-ethoxy sulfate.
Description
Normally tacky and pressure-sensitive water-borne emulsion polymer adhesive
compositions suitable for application to plasticized polyvinyl chloride
film, having excellent retention of peel force strength, are emulsion
polymerized and compounded in the essential absence of sodium and lithium
cations.
BACKGROUND OF THE INVENTION
This invention relates to pressure sensitive adhesive compositions
particularly suited for use as permanent adhesives on flexible vinyl
substrates is such as plasticized polyvinyl chloride films.
Flexible vinyl films coated with pressure sensitive adhesive are used in
many applications such as decorative vinyl laminations, decals, signage,
and specialty tapes. Solvent-borne pressure sensitive adhesives have
traditionally been employed in these applications. Environmental, health
and safety concerns have encouraged development of new aqueous adhesive
systems to replace traditional solvent based adhesives. The adhesive
performance requirements for flexible vinyl film applications dictate that
pressure sensitive adhesive coating exhibit sufficient tack and anchorage
to both the vinyl film and substrate to prevent lamination failure in the
intended application. The adhesive must also possess sufficient cohesive
strength to prevent adhesive flow during vinyl film converting, storage,
and use. Additionally, the aforementioned adhesive properties must not
fall below required performance parameters while in contact with the
plasticized vinyl film.
Diminution of pressure sensitive adhesive performance measurements while on
flexible vinyl film is a well known problem. Flexible vinyl films are
complex mixtures containing polyvinyl chloride resin, fillers,
plasticizers, stabilizers, lubricants and other processing aids. The
plasticizers are known to migrate from the flexible vinyl film into the
adhesive coating and degrade pressure sensitive adhesive performance
(Graziano, L. C. and Sjostrand, E., "Development of Acrylic Latex Pressure
Sensitive Adhesive for Plasticized PVC Films", Journal of Plastic Film &
Sheeting, Vol. 2, April 1986, pages 95-110).
Specific monomer combinations that yield specific copolymer compositions
have been proposed as having superior resistance to plasticizer migration
and retention of initial adhesive properties. For example, according to
Mudge U.S. Pat. No. 4,822,676, emulsion polymers containing specific
compositions of vinyl ester, acrylic ester, ethylene, tertiary octyl
acrylamide, and monocarboxylic acid monomers afford a copolymer with
superior performance when coated on plasticized polyvinyl chloride film.
Mudge uses the group IA metal cation sodium found in sodium acetate,
sodium alkyl aryl polyethylene oxide sulfate, and sodium formaldehyde
sulfoxylate.
U.S. Pat. No. 5,316,762 Kiamil describes a water resistant medical adhesive
polymerized in the presence of ammonium salt surfactants in the absence of
metal salts. This adhesive has good tack and is not further compounded
with tackifiers or plasticizers.
According to Warson, Synthetic Resin Emulsions, Surfactants and
Stabilizers, 1972, using ammonia (as the alkali) in making soaps
(surfactants) as salts of fatty acids has the advantage that on drying an
emulsion no water-soluble materials remain but only an insoluble fatty
acid remains. The volatility of ammonia has certain disadvantages,
especially when used with polymer emulsions, since loss of ammonia will
cause a drop in pH, and may lead to instability. During drying of a film
premature instability may occur, or as with a coating on steel, "flash"
corrosion, caused by premature drop in pH. In consequence, ammonia is
often replaced by amines. The removal of group IA metals from a
polysiloxane coating by ion exchange to improve adhesion under conditions
of high humidity is described in U.S. Pat. No. 5,069,942 Anderson.
SUMMARY OF THE INVENTION
It has now been found that coater ready emulsion polymer pressure sensitive
adhesives prepared in the substantial absence of common metal cations of
group IA, such as sodium, possess superior retention of initial peel force
properties when coated and aged on flexible vinyl film. In this invention
the phrase "substantial absence" means less than about 150 parts sodium
cation or lithium cation per million parts dry weight of the adhesive
film. These trace amounts of cation are from sodium formaldehyde
sulfoxylate chaser chemicals used in the emulsion polymerization step. We
have found that cations may be present up to 200 parts per million parts
adhesive film dry weight without deleterious effect on properties.
DESCRIPTION OF THE INVENTION
Emulsion polymers are commonly prepared with salts. These salts may be
initiators (i.e. persulfate salts), ionic surfactants, buffers,
thickeners, and alkalis. Ammonium, sodium, or potassium salts are commonly
used in the commercial manufacturing of emulsion polymers. The effect of
cation type on adhesive performance was demonstrated by selection of
different ionic initiators, reaction buffers, ionic emulsifiers, and
basification agents when polymerizing and formulating a coater ready
aqueous emulsion pressure sensitive adhesive.
In the Examples all measurements are in the metric system unless otherwise
indicated. All references mentioned herein are specifically incorporated
by reference.
EXAMPLE 1
An aqueous acrylic emulsion pressure sensitive adhesive composition
prepared or "emulsion polymerized" in the absence of group IA metal
cations and containing only ammonium cations was prepared as follows.
______________________________________
grams
______________________________________
REACTOR CHARGE pphm
Deionized Water 50.0 815.2
MONOMER EMULSION pphm
Deionized Water 25.0 407.6
RHODAPEX CO-436 2.0 32.6
Aqua Ammonia 29% 1.0 16.3
Acrylic Acid 2.0 32.6
2-Ethylhexyl Acrylate
45.0 733.7
n-Butyl Acrylate 45.0 733.7
Styrene 8.0 130.4
INITIATOR pphm
Ammonium Persulfate 1.0 16.3
RINSE WATER pphm
Deionized Water 5.0 81.5
COMPOUNDING pph
Emulsion Polymer C5708-136
100.0
Aqua Ammonia 29% 0.8
PLURONIC L-101 3.0
______________________________________
Deionized water had a conductivity of 1.0 .mu.S or less.
RHODAPEX CO436 surfactant is an ammonium salt of
nonylphenol4-ethoxy-sulfate (58 wt %) in water (27 wt %) and ethanol (15
wt %) supplied by RhonePoulenc.
PLURONIC L101 is a nonionic ethylene oxide propylene oxide block polymer
wetting agent supplied by BASF Corporation.
A jacketed PYREX reactor equipped with nitrogen purge, stirrer, and
addition ports was charged with deionized water which was heated to
80.degree. C. A monomer emulsion was prepared. The initiator was added to
the reactor and the monomer emulsion was added at a constant rate over a
three hour period. The resulting emulsion polymer was held at 85.degree.
C. for one hour then cooled to 30.degree. C., filtered through cheese
cloth and labeled C5708-136.
Emulsion polymer C5708-136 afforded a nonvolatile content of 55.2 wt %, pH
of 5.7, Brookfield RV viscosity of 60 cps at 20 rpm, 0.18 grams of
filtered coagulum on cheese cloth, 9 ppm on 100 mesh filter and 10 ppm on
200 mesh filter.
A coater ready pressure sensitive adhesive was made by further compounding
C5708-136 emulsion polymer with ammonia and nonionic PLURONIC wetting
agent to afford pressure sensitive adhesive C5708-142A having a pH of 9.4
and Brookfield viscosity of 570 cps at 20 rpm.
EXAMPLE 2
An aqueous acrylic emulsion pressure sensitive adhesive composition made
exclusively with group IA metal cations and containing sodium cations was
emulsion polymerized as follows.
______________________________________
grams
______________________________________
REACTOR CHARGE pphm
Deionized Water 50.0 815.2
MONOMER EMULSION pphm
Deionized Water 23.4 380.9
RHODAPEX CO-433 4.0 65.2
Sodium Hydroxide 0.7 11.1
Acrylic Acid 2.0 32.6
2-Ethylhexyl Acrylate
45.0 733.7
n-Butyl Acrylate 45.0 733.7
Styrene 8.0 130.4
INITIATOR pphm
Sodium Persulfate 1.0 16.3
RINSE WATER pphm
Deionized Water 5.0 81.5
COMPOUNDING pph
Emulsion Polymer C5708-138
100.0
Sodium Hydroxide Solution 17%
1.6
PLURONIC L-101 3.0
______________________________________
Deionized water had a conductivity of 1.0 .mu.S or less.
RHODAPEX CO433 is a sodium salt of nonyl4-ethoxy-sulfate solution (28 wt
active) in water (72 wt %) supplied by RhonePoulenc.
PLURONIC L101 is a nonionic ethylene oxide propylene oxide block polymer
wetting agent supplied by BASF Corporation.
A jacketed PYREX reactor equipped with nitrogen purge, stirrer, and
addition ports was charged with deionized water which was heated to
80.degree. C. A monomer emulsion was prepared. The initiator was added to
the reactor and the monomer emulsion was added at a constant rate over a
three hour period. The resulting emulsion polymer was held at 85.degree.
C. for one hour then cooled to 30.degree. C., filtered through cheese
cloth and labeled C5708-138.
Emulsion polymer C5708-138 afforded a nonvolatile content of 55.2 wt %, pH
of 5.1, Brookfield RV viscosity of 60 cps at 20 rpm, 0.24 grams of
filtered coagulum on cheese cloth, 7 ppm on 100 mesh filter and 9 ppm on
200 mesh filter.
A coater ready pressure sensitive adhesive was made by further compounding
C5708-138 emulsion polymer with the ammonia and nonionic PLURONIC wetting
agent to afford pressure sensitive adhesive C5708-143 having a pH of 8.7
and Brookfield viscosity of 250 cps at 20 rpm.
EXAMPLE COMPARISON
The coater ready pressure sensitive adhesives of Examples 1 and 2 were
coated on H. P. Smith POLYSILK 8024 release liner at a film thickness of
1.0.+-.0.1 mil and transferred to a 3 mil white calandered vinyl film. The
pressure sensitive adhesive properties of the films were evaluated in
accordance with Pressure Sensitive Tape Council (PSTC) 1 Peel Force
measurement with a 15 minute dwell and PSTC 7 holding power shear test
methods and a Quick Stick PSTC-5 measurement after 24 initially and after
aging the laminations eight days at 158 F.
______________________________________
Example 1 Example 2
Ammonium PSA
Sodium PSA
______________________________________
Initial Adhesive Performance
180.degree. Peel Force (lbs/in)
15 min. dwell 2.1 0.4
24 hr dwell 2.3 1.8
Quick Stick (lbs/in)
4.1 0.4
Holding Power (Mins.)
2 38
Aged Adhesive Performance
180.degree. Peel Force (lbs/in)
15 min. dwell 1.3 0.1
24 hr dwell 1.8 0.1
Quick Stick (lbs/in)
1.7 0.2
Holding Power (Mins.)
7 34
______________________________________
This comparison demonstrates the influence that cation type has on pressure
sensitive adhesive performance. The adhesive of example 1, emulsion
polymerized and compounded in the absence of Group IA metal cation
exhibited a PSTC 1 peel force retention of 78% (24 hr dwell ). The
adhesive emulsion polymerized and compounded exclusively with sodium
cations exhibited a PSTC 1 peel force retention of only 6% (24 hr dwell).
This example confirms that emulsion polymerization in the absence of sodium
cation provides a permanent pressure sensitive adhesive having better than
70% peel force retention on aging.
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